At present, piezoelectric inkjet print heads are widely used. The print head module of an ordinary piezoelectric inkjet print head is a piezoelectric device. Each of the nozzles of the print head is driven by a sheet of piezoelectric ceramic plate. When a voltage of the fire pulse is applied to a corresponding piezoelectric ceramic plate in a certain controlled switching rate, the piezoelectric ceramic plate is energized to offset outward so as to form a negative pressure wave so that ink is drawn into a chamber. After undergoing a constant duration of pulses, the voltage of the fire pulse is removed in a certain controlled switching rate. Since the wall of the chamber is expandable and shrinkable, the total positive pressure waves propagate forwardly to cause the nozzle to jet ink droplets.
The voltage wave of the fire pulse applied to the actuation member of the piezoelectric ceramic plate to induce deformation thereof is slightly different from one type of a nozzle to another. A typical voltage wave of the trapezoidal fire pulse is shown in FIG. 1. The trapezoidal fire pulse can be characterized by four parameters: a fire pulse amplitude (FPA), a fire pulse width (FPW), a rise time (RT) and a fall time (FT). All of the four parameters of the trapezoidal fire pulse may influence the initial velocity and volume of the jetted ink droplet as well as the uniformity of all ink droplets, ultimately influencing the printing quality.
To obtain optimum printing effects, different voltage wave of the trapezoidal fire pulse are required for different print heads, ink and printing materials. Thus, the parameters of the output fire pulse are required to be flexibly adjustable by the device for generating the fire pulse to drive the piezoelectric inkjet print. That is, the fire pulse amplitude, the fire pulse width, the rise time and the fall time of the voltage waveform of the generated trapezoidal fire pulse can be set in real time. In the meanwhile, the device for generating the fire pulse should be as simple as possible in structure while maintaining a high accuracy.
A device for generating the fire pulse generally used in the conventional system for controlling a print head is shown in FIG. 2. In FIG. 2, a voltage regulator is controlled by a pulse amplitude control signal to generate a high voltage DC signal V+ having the amplitude of a fire pulse required to be output. Then, the signal V+ is switched by a half bridge converting circuit so that a fire pulse constituted by the signal V+ and an earth voltage is output. Thus, a voltage waveform signal of the fire pulse is generated to drive the print head. The amplitude parameter of the generated fire pulse can be flexibly adjusted by the device for generating the fire pulse as shown. However, the rise and fall times of the generated fire pulse are determined by the output impedance and the equivalent capacitance of the load of the device for generating the fire pulse together. Such a structure of the device for generating the fire pulse results in a fluctuation of the generated fire pulse waveform due to different loads, and therefore has some influence on the final printing quality.